6.6-stable review patch. If anyone has any objections, please let me know.
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From: Pavel Begunkov asml.silence@gmail.com
[ Upstream commit dc12d1799ce710fd90abbe0ced71e7e1ae0894fc ]
The UINT_MAX work item counting bias in io_req_local_work_add() in case of !IOU_F_TWQ_LAZY_WAKE works in a sense that we will not miss a wake up, however it's still eerie. In particular, if we add a lazy work item after a non-lazy one, we'll increment it and get nr_tw==0, and subsequent adds may try to unnecessarily wake up the task, which is though not so likely to happen in real workloads.
Half the bias, it's still large enough to be larger than any valid ->cq_wait_nr, which is limited by IORING_MAX_CQ_ENTRIES, but further have a good enough of space before it overflows.
Fixes: 8751d15426a31 ("io_uring: reduce scheduling due to tw") Signed-off-by: Pavel Begunkov asml.silence@gmail.com Link: https://lore.kernel.org/r/108b971e958deaf7048342930c341ba90f75d806.170543866... Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- io_uring/io_uring.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index 1cc4c7b05949..ea772a02c140 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -1339,7 +1339,7 @@ static inline void io_req_local_work_add(struct io_kiocb *req, unsigned flags) nr_tw = nr_tw_prev + 1; /* Large enough to fail the nr_wait comparison below */ if (!(flags & IOU_F_TWQ_LAZY_WAKE)) - nr_tw = -1U; + nr_tw = INT_MAX;
req->nr_tw = nr_tw; req->io_task_work.node.next = first;